52 JOURNAL AND PROCEEDINGS 



ordinary gray fracture of cast iron. In Plate 3 there is shown 

 the crytalline fracture of a white iron test bar after it has 

 been annealed. The chemical, composition of the white iron 

 varies somewhat in accordance with the class of castings that 

 are being made, principally with respect to the Silicon con- 

 tent. This element may be as low as 0.45% in castings of 

 heavy section, and as high as 1.00% in castings of lighter 

 weight. Sulphur should be kept as low as possible, the usual 

 limit set being 0.06%. Phosphorus may be allowed to run to 

 0.20%, but better results can be obtained if it does not rise 

 above 0.16%. Very small percentages of Sulphur and Phos- 

 phorus profoundly influence the annealing qualities of the 

 iron, and an excess of either may entirely prevent the anneal 

 from being effective. 



The :^mieal — After the castings have been cleaned from 

 adherent sand, they are placed in white iron saggers, or pots 

 of convenient size, and the spaces between them filled in by a 

 packing consisting of rolling mill scale, slag, iron turnings 

 and other similar material. The purpose of the packing is 

 merely to prevent the hot gases of the annealing ovens from 

 playing directly upon the castings, and not, as was formerly 

 supposed, to supply oxygen for the decarbonization of the 

 iron. Any material may therefore be used which is 

 sufficiently cheap, is economical to handle, and will readily 

 conduct the heat to the castings. The pots having been filled 

 are transferred to the annealing ovens, wliich are rectangular 

 chambers equipped for continuous firing, and provided v\ith 

 draft flues necessary to the even distril)Ution of the beat 

 throughout the entire space. Various fuels are used — oils, 

 gas, lump or powdered coal — and good results may be 

 obtained with any of them if they are burned to advantage. 



The duration of the annealing process depends upon the 

 size of the casting and the degree of excellence required, but 

 it may be considered as averaging one week from the closing 

 of the ovens to the discharging of the iro!i. The actual 

 period of firing is usually frorii 90 to 100 hours, and is re- 

 quired by standard specifications to continue fully 60 hours 



